Why does a catalyst need to be activated?
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Why does a catalyst need to be activated? For the catalysts used in vinyl chloride synthesis, why is hydrogen chloride required to activate the newly replaced catalysts? What is the purpose of activation? If the catalyst is flipped, is a second activation required?
1. Moisture in the catalyst is removed by adding hydrogen chloride. 2. Acetylene reacts more readily with the catalyst than hydrogen chloride; therefore, hydrogen chloride should be introduced first to saturate the catalyst, otherwise acetylene will undergo irreversible reactions with the catalyst, leading to its poisoning and loss of effectiveness. 3. After the catalyst was flipped, we also carried out single-pass activation of the catalyst with hydrogen chloride.
Hydrogen chloride activation is not intended to remove moisture from the catalyst, as it should already be dried to the appropriate standard before being subjected to hydrogen chloride activation. The main reason for using hydrogen chloride for activation is that acetylene easily reduces mercuric subchloride in the catalyst to calomel or mercury, causing the catalyst to lose its activity very quickly ； Moreover, this process is irreversible; it is what is known as catalyst poisoning. Purpose: To fill the pores of the catalyst with hydrogen chloride to a nearly saturated level, thereby minimizing the impact of acetylene on the catalyst. After handling the catalyst, it needs to be dried and activated, which is highly beneficial for the catalyst.
The synthesis mechanism of vinyl chloride is not such that acetylene first reacts with mercuric chloride to form chloro-mercuric vinyl chloride; since chloro-mercuric vinyl chloride is very unstable, it decomposes upon contact with hydrogen chloride to yield vinyl chloride.
The views of the above-mentioned individuals are all reasonable in their own way. The main functions of using hydrogen chloride to treat catalysts: 1) Utilizing dry hydrogen chloride to absorb trace amounts of moisture in the catalyst, thereby preventing catalyst caking and corrosion of equipment pipelines ； 2) Due to the large surface area of the catalyst, it can easily adsorb various gases. To maintain its activity, hydrogen chloride is introduced first to saturate it fully, thereby preventing excessive acetylene from causing catalyst poisoning.